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Prying Open the Pigpen Cipher

Today, your local, run-of-the-mill inmate – say, inmate 3087A, passes a note along to inmate 2065B. Circa 1863, a Union prisoner of the Confederate Army secretly sends a letter describing his whereabouts to his fellow troops. In the early 18th century, a Masonic text, some letter of correspondence or sacred order, is recorded by one of the most interesting and elusive societies to have ever existed.

Separated by generations, all three instances share a single commonality – the inmate, soldier and Freemason would each be able to read each other’s notes despite the fact that, for the sake of secrecy, they are not writing in the standard English alphabet. No, they are not drawing pictures (although they kind of are), and no, they are not simply writing in a different language (although they might as well be). What they are in fact doing is employing a cipher system which dates back to the dawning of Freemasonry. This cipher, for the time being, can be referred to as the Masonic or Rosicrucian cipher (Pratt, 1942).

The Problems with Secure Communication

Unfortunately for the prisoner, soldier and Freemason, none of their messages are relatively secure. Surely, an inmate has plenty at stake if the contents of his message are intercepted – perhaps a few more years to his sentence. And of course, the military application of a cipher should ensure a safeguard against enemy eyes. The concept is pretty simple. Ciphers or codes are born from secrecy, serve secrecy, and by way of function, are themselves kept secret. So why is it that you, I, or even a school child can decipher the very same coding system used by one of the most cryptic societies to have ever existed? It’s a little embarrassing.

To answer this question, an understanding of the cipher’s historical context and mechanical construction is necessary. True to its name, the masonic cipher was supposedly created, and knowingly employed, by the Freemasons. Freemasonry, as it is called, falls under the category of “secular fraternal organization” (MacNulty, 2006 p. 9). To define it in more concrete terms, “…it is a society of religious men in the sense that it requires its members to believe in the existence of a ‘Supreme Being’” (MacNulty, 2006 p. 9). In accordance with their “….commitment not to reveal certain things,” the fraternity created its own cipher, which bares resemblance to that of the ancient Knights Templar (MacNulty, 2006 p. 269). Its first date of use, however, remains unknown due to the fraternity’s secrecy (Pratt, 1942).

Pigpen Cipher

Interestingly enough, the cipher is a simple substitution cipher in which each letter of the alphabet in use is assigned a different letter or symbol (Butler & Keeney, 2001). Both in theory and practice, this type of cipher is considerably weak, especially if the construction of the cipher involves a notable pattern, which the Freemason’s cipher does.

Example of a pigpen cipher and its deciphered message.

Its construction, though best explained visually, can be defined as the arrangement of an alphabet into a series of grids. Though there exist many variants of the cipher, the masonic cipher follows the illustrated principle. The twenty-six letters of the alphabet are arranged into “two Tic-Tac-Toe grids and two diagonal variations of the grid” (Butler & Keeney, 2001 p.159).

Because each pair of grids is identical in shape and form, one of each pair is distinguished by the placement of dots within each cell of that grid. This results in four differing grids with one letter in each individual cell: one tic-tac-toe grid with dots, one without, one diagonal grid with dots, and another without. Because the grids represent pigpens or tic-tac-toe grids, the cipher is more commonly and creatively referred to as the pigpen cipher, or the tic-tac-toe cipher (Butler & Keeney, 2001).

The cipher is employed by representing each plaintext letter with the cell surrounding it, resulting in a message encoded by a series of varying, though similar, geometrical shapes as shown below.

The construction of the pigpen cipher. The cipher text here reads “Mary I love you too.”

The simplicity of the pigpen cipher allows for several important strengths. Firstly, and perhaps most importantly, the cipher is considerably easy to learn. Minimal math is involved, little time is consumed, and the symbols are only as complicated as you make them out to be.

Secondly, the pigpen cipher is relatively easy to memorize. Because the code can be committed to memory, a tangible and potentially intercepted key need not exist. This is the problem with many ciphers throughout history, for their keys would be intercepted, thus making that current key useless in practice (Kahn, 1996). The cipher is also very versatile. Because the construction, order of letters and orders of the grids and cells is entirely up to the cryptographer, many variations of the cipher exist.

Simplicity: Strength and Weakness

Unfortunately for those using the cipher, simplicity also gives way to weakness. For starters, the cipher is easy to recognize if one is familiar with its construction. Notice a series of slightly varying symbols and voila, you can immediately attempt decryption. At said stage of decryption, one might realize that it is almost as easy to crack as it is to recognize (obviously a major fault in the cryptographic world). Simply arrange the cells into their respective grids, and through intuition of trial-and-error and frequency analysis (in which you assume the most common symbols correspond to the most common letters in the English language), arrange the letters until a coherent message is formed.

So why, then, did the Freemasons encourage this weak method of encryption? Simply put, back in the 1700s, you only had to hide text from those who could actually read. Provided that someone with prying eyes was literate, the fact that the cipher was relatively new to the era also served as a buffer for decryption. Hopefully now, given a message in pigpen, you or I would have some luck decrypting it. In the 1700s, however, the cipher would surely stump us for lack of familiarity.

In fact, in December of 1863, the pigpen cipher stumped the Union army (Kahn, 1996). After intercepting an envelope addressed to a rebel agent, Postmaster Abram Wakemen of New York turned the letter over to the Secretary of War. The letter, as you might have guessed, was entirely enciphered in “…a complicated mixture of symbol ciphers” (Kahn, 1996 p.218). Unable to decrypt the intended message, the War Department handed the responsibility to the “Sacred Three.”

David Homer Bates, Albert B. Chandler and Charles A. Tinker, the accomplished cryptographers referred to as the “Sacred Three,” first noticed the five different kinds of signs used in the text (representing the five different types of grids used). They also had some luck in that commas separated each word from another, as would spaces in plaintext. Whoever encrypted the message was even courteous enough to leave some plaintext in the letter. But most importantly, in a flash of insight, Bates recognized the use of a pigpen cipher, “which had been used as a price marker in the Pittsburgh store in which he had worked as a boy” (Kahn, 1996 p.219).

By focusing on the heading, which included the standard date and address from which the letter was sent, the three deciphered the message within four hours “with the President hovering about anxiously” (Kahn, 1996, 219). Despite the presidential motivation, this argues against the security of the cipher. As it turns out, the message included details regarding the manufacture of Confederate plates for printing money, all of which were promptly seized shortly after decryption.

Evolutions in Cipher

Flash-forward by a century and a half, and today the pigpen cipher has made its mainstay in the prison and crime underworld, where it persists and evolves as inmates and criminals avoid detection by the authorities. Surprisingly, the cipher need not be written, for it can be spoken. In the spoken variation, each letter of the alphabet is assigned a number. The grids of the pigpen cipher are then used to arrange the letters in some order, and numbers are assigned one per cell from left to right across all of the grids. An inmate, in order to express himself, would simply shout the numbers from his cell, essentially spelling out all of the words he wishes to communicate (Butler & Keeney, 2001).

The “Clock Code” method has also evolved from the pigpen cipher. Around the perimeter of a single grid, twenty-four letters are arranged, with two in the center. The letters are each marked by their orientation in respect to the center of the grid, and a time of day is designated, which designates where A would be, followed in succession by each letter of the alphabet. This variation is best noted for its versatility (Butler & Keeney, 2001).

The pigpen cipher, therefore, has persisted by its convenience and flexibility, rather than security. Though borne out of secrecy, it is forged in simplicity, and is thus used today as a quick substitute for plaintext conversations, or stimulating puzzle for schoolchildren. Despite its relative lack of complexity and challenge, it is interesting to note its use and relevance throughout the centuries and in today’s modern society. That said, in preparation for a run-in with the law, initiation into Masonic society, or capture by Confederate troops (the likes of which deserves a blog post all its own), practice the pigpen cipher for yourself here, or pick up the nearest children’s spy novel in which you’ll be sure to find some example of this simple cipher.

This post is part of a series of essays on the history of cryptography produced by students at Vanderbilt University. The students wrote these essays for an assignment in a first-year writing seminar taught by mathematics instructor Derek Bruff. The essays are shared here, in part, to give the students an authentic and specific audience for their writing. For more information on this cryptography seminar, see the course blog.

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Wonders & Marvels is no longer being updated. This site was created by award-winning author Holly Tucker, who also served as Editor-in-Chief, and ran for over 9 years (2008-2017). We wish to thank the many writers and historians who contributed articles to Wonders & Marvels, including and especially our regular contributors.